High-frequency electric discharge device and circuits associated therewith



Feb. 15, 1955 MCARTHUR 2,702,349

HIGH'FREQUENCY ELECTRIC DISCHARGE DEVICE AND CIRCUITS ASSOCIATED THEREWITH Filed Feb. 15, 1951 2 Sheets-Sheet 1 Fig. l;

Inventor": Ell meP-D. Me Arthur,

His Attorney.

Feb. 15, 1955 E. D. M ARTHUR 2,702,349

HIGH-FREQUENCY ELECTRIC DISCHARGE DEVICE AND CIRCUITS ASSOCIATED THEREWITH Filed Feb. 15 1951 2 Sheets-Sheet 2 TIME 1 1 ll l? 2 2 HIGH FREQUENCY W SIGNAL l w i Hll I "fi X "ii z zz MODULAT/NG l [/L;LE7Z?0DES CONTROL A JE EQI /CATHODE HJJJ Inventor:

Elmer D. McArthur", by 7%! .4fi His Attovneg- United States Patent l-HGH-FREQUENCY ELECTRIC DISCHARGE DE- VICE AND CIRCUITS ASSOCIATED THEREWITH Elmer D. McArthur, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application February 15, 1951, Serial No. 211,086

7 Claims. (Cl. 250-36) My invention relates to high frequency electric discharge devices and associated circuits, and more particularly to electric discharge devices and circuits which produce a velocity modulation of an electron discharge during the time of electron transit between electron emitting and electron receiving surfaces.

High frequency electric discharge devices which have heretofore employed the phenomenon of velocity modulation of an electron discharge in their operation, may, in general, be classified as being either of the Klystron type or the positive-grid Barkhausen type. In the Klystron type of discharge device, an electron discharge or stream passes through a first cavity resonator, customarily called a buncher resonator, into a drift tube wherein the electrons tend to bunch together as they travel down the tube. A second cavity resonator, customarily called a catcher resonator, is located at the end of the drift tube and is energized by these bunches or pulses of electrons. In a modification of this basic Klystron type discharge device customarily called a reflex Klystron, a reflector electrode is located at the end of the drift tube and repels the bunches of electrons back to the first cavity resonator which functions both as the buncher resonator and the catcher resonator. Since the amount of power required to produce the bunching effect is relatively small compared with the amount of energy delivered by the electron stream to the catcher resonator, such Klystron devices can be operated as power amplifiers, or a small fraction of the energy developed in the catcher resonator can be diverted to excite the buncher, thus producing an oscillator. Theoretically, the maximum possible efliciency of such Klystron devices is about 58% although practical efficiencies are much less than this figure.

The operating conditions for such Klystron devices, are very critical. The anode voltage, electron stream current, frequency of resonance of the resonators, ratio of buncher resonator to catcher resonator voltages, and the coupling of the load to the catcher resonator must be carefully adjusted for optimum results. The bunching of the electron stream should be maximum at the location of the catcher resonator, and this bunching is affected by anode voltage, the length of the drift tube, and the exciting voltage supplied to the buncher resonator.

In positive-grid Barkhausen devices a control electrode located intermediate an electron emitting cathode and an anode is operated at a positive potential with respect to both the cathode and the anode. Under these conditions, most of the electrons attracted by the control electrode pass between the interstices of the control electrode toward the anode, but because of the negative potential of the anode With respect to the control electrode, these electrons are returned back toward the control electrode to oscillate about the control electrode at a frequency determined by the electrode voltages and the distances involved. These electrons oscillate back and forth between the cathode and anode sides of the control electrode structure with the result that oscillatory energy is delivered into an electrical circuit associated with this control electrode. All of the electrons leaving the cathode, however, do not contribute to this oscillatory energy delivered to the control electrode circuit. Some of the electrons are immediately captured by the control electrode, others are accelerated sufliciently to reach the anode directly while still others are returned back to the cathode. In the aggregate however, there is net resultant energy available to sustain oscillations in the control electrode circuit and there is a tendency for the majority of the electrons in the tube to be oscillating together at any particular instant of time. Both the theoretical and practical efficiencies attainable with such Barkhausen-type devices are much less than that attainable with Klystron type devices. An efliciency in the neighborhood of 2 percent is considered quite favorable for such Barkhausen oscillators.

In velocity modulated electric discharge devices of the reflected stream type such as the reflex Klystron or the positive-grid Barkhausen device, it is quite difficult if not impossible to operate such devices as an amplifier of high frequency energy since the output voltage is taken from the single cavity resonator associated therewith and no other means are provided for supplying an input high frequency signal to the device. Such reflected stream velocity modulated devices normally function, therefore, only as oscillators. In addition, such devices normally operate only upon the basis of a velocity modulation of the electron stream with little attention being given to a direct space charge modulation of the electron stream current passing from cathode to anode.

Accordingly, an object of my invention is to provide an improved high frequency electric discharge device of the reflected electron stream type.

Another object of my invention is to provide a high frequency electric discharge device of the reflected electron stream type in which adjustment of the operating conditions is not as critical as in conventional Klystron type discharge devices.

Another object of my invention is to provide an electric discharge device of the reflected electron stream type wherein the frequency of operation does not depend to any appreciable extent upon the anode voltage.

An additional object of my invention is to provide an electric discharge device of the electron stream reflecting type in which a modulating electrode is employed both to modulate the velocity of the electron stream and to control the magnitude of current passing to a current collecting electrode of the device.

A further object of my invention is to provide an electric discharge device of the electron stream velocity modulating and reflecting type in which the output energy is taken from a circuit associated with a current collecting electrode distinct from the electron stream velocity modulating electrode of the device.

A further object of my invention is to provide an electric discharge device of the electron stream reflecting type which can be used either as an amplifier, oscillator or detector of high frequency electric energy.

A still further object is the attainment of a device in which the output current modulation is accomplished with a minimum of input driving power so as to enable the production of a device which has a theoretical maximum efiiciency in the neighborhood of 64%.

In fulfillment of this latter object, it is a still further ob ect of my invention to provide a high frequency electric discharge device in which control of an electron current passing from a cathode to an anode is achieved by electrodes located between the cathode and a generated space charge region rather than on the opposite side of the space charge region, whereby an unusually large control of anode current is produced with little input signal energy.

In general, my invention comprises a high frequency electric discharge device of the electron stream reflecting type wherein a modulating electrode, located intermediate a thermionic cathode and a reflector electrode, is maintained at a high positive potential with respect to both the cathode and the reflector electrode. The modulating electrode is spaced a proper distance from the cathode and the reflector electrode such that electrons emitted from the cathode are velocity modulated in accordance with a high frequency signal voltage supplied to the modulating electrode and, in addition, caused to oscillate about the modulating electrode in accordance with a predetermined cycle and then to arrive at an anode located in the vicinity of the reflector electrode in electron bunches or pulses in accord with the amplitude'and frequency of the high frequency signal voltage. Depending upon the relative magnitudes of the operating potentials applied to the cathode, modulating electrode, reflector electrode and anode, the device may be operated at the anode current cut-off point as in a class B amplifier, or may be biased such that current flows only with a strong input signal voltage so as to simulate a class C amplifier. By including a regenerative coupling from the output circuit to the input circuit of the device, operation as an oscillator may be obtained.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims. My invention itself, however, together with further objects and advantages thereof may best be understood by reference to the following description taken in connection with the accompanying drawing in which Fig. 1 is a cross-sectional view of one embodiment of my invention together with a diagrammatic indication of operating potentials supplied thereto, Fig. 2 is a similar sectional view of a modification of the device of Fig. 1 whereby the electron stream forming portion of the electric discharge device is adapted to be plugged into associated cavity resonators and means are included for adapting my invention for use as an oscillator. Fig. 3 is a simplified diagrammatic representation of the movement of the electron stream within the discharge device of my invention when a high frequency signal is supplied to a modulating electrode thereof, and Fig. 4 is a further simplified schematic diagram of the discharge device and circuit of my invention helpful in the explanation of the operation of my invention.

Referring to Fig. 1, I have shown my invention in one form as comprising an electric discharge device including a cylindrical cathode 11 and a cylindrical anode 12, the cathode having an electron emitting end surface 13 ali ned to an electron receiving end surface 14 of collecting anode 12. A pair of electron stream modulating electrodes 15 and 15a are located intermediate electron emitting surface 13 and electron receiving surface 14 to influence an electron stream passing from sur face 13 to surface 14. Modulating electrodes 15, 1511 are preferably arranged in spaced planar alignment, as indicated. and connected to define a central gap 16 of an annular input cavity resonator 17. Input coupling means such as loop 18 fed by coaxial cable 19 are provided for supplying a high frequency signal voltage to excite input resonator 17. In order to assist in the formation of a beam of electrons directed toward the electron receiving surface 14 of the anode 12, I preferably also provide a cylindrical focusing member 20 which surrounds the cathode 11 andis secured in spaced relation thereto by an annular insulating bead 21. The focusing collar member 20 preferably supports a beam current controlling electrode 22 which is located in the path of the electron stream passing from cathode 11 to anode 12.

An output cavity resonator 23, which may conveniently be an axially extending cylindrical resonator formed by an outer cylinder 24 located in concentric spaced relation with the cylindrical wall of anode 12, is arranged to be excited by an electron stream passing to the electron receiving surface 14 of the anode 12 through a central gap 25 of output resonator 23. A reflector electrode 26 supported in conductive relation with the outer cylinder 24 of resonator 23 enables the passage of electrons to anode 12 and also functions to aid in controlling the reflection of the electron stream in a manner to be described hereinafter. Energy may be extracted from output resonator 23 by any suitable hi h frequency coupling means such as a coupling probe 27 and a coaxial cable 28. Output resonator 23 is preferably made tunable by such means as an annular tuning plunger 29 which preferably includes an embedded insulating washer 30 in order to enable different unidirectional potentials to be supplied to the anode 12 and the outer cylinder 24 of resonator 23. Alternatively, high frequency choke type tuning elements which make contact to only one resonator wall may be employed for this purpose.

Proper operating voltages for device 10 may be supplied by a source of unidirectional potential such as battery 31. As indicated by the relative positions of the tap connections 32, 33, 34, from device 10 to battery 31, the input cavity resonator 17 and consequently the modulating electrodes 15 and 15a are maintained at h1gh positive potential with respect to the focusing member 20 and control electrode 22 which, in turn, are held at a slightly positive potential with respect to cathode ll.-

Similarly, input resonator 17 and modulating electrodes 15 and 15a are held at a high positive potential with respect to outer cylinder 24 and reflector electrode 26 of output resonator 23. Anode 12 is held positive with respect to reflector electrode 26 and may even be positive with respect to resonator 17. This high potential difference between reflector electrode 26 and anode 12 is the source of output power developed in output resonator 23. Alternating voltage for heating the cathode 13 may be supplied to a heater filament 37 through a filament supply transformer 37a.

For class B operation, the voltage supplied to reflector electrode 26 is adjusted just to the point of anode current cut-ofl. With apparatus such as described in Fig. 1, this cut-off point usually occurs when the reflector electrode 26 is connected as indicated by the position of tap 33 to a voltage slightly negative with respect to the voltage supplied to cathode 13. For class C operation tap 33 is moved to a more negative point on battery 31 so that the device is biased somewhat below the anode current cut-ofi point.

The distance from the cathode surface 13 to the modulating electrodes 15 and 15a and from these latter modulating electrodes to the reflector electrode 26 must be such that for the particular operating voltages involved the time of transit of electrons across the region associated with these electrodes is equal to a predetermined portion of the time necessary to complete one cycle of high frequency signal voltage supplied to the input resonator 17, as will be more fully explained hereinafter. Where the desired distance between the control electrode 22 and reflector electrode 26 is close to the optimum width of input resonator 17, simple insulating spacing means such as insulating washer 38 hermetically sealed between a shoulder 39 of focusing member 20 and one Wall of input resonator 17 and a similar insulating washer 40 sealed between an opposite wall of resonator 17 and a wall of output resonator 23 may be provided to hold the entire assembly together and hermetically enclose the various electrodes of the device. An annular dielectric sealing member 41 pervious to electromagnetic fields and sealed between anode 12 and outer cylinder 24 is preferably also provided in order to enable the electron discharge region of device 10 to be maintained in an evacuated condition.

Where the desired distance between the control electrode 22 and the reflector electrode 26 is considerably greater than the optimum width of input resonator 17, a construction such as shown in Fig. 2 may conveniently be employed. In Fig. 2 a discharge device 10:: is illustrated wherein a pair of cylindrical modulating-grid supporting members 42 and 42a which serve to support and make connection to modulating grids 15 and 15a respectively are included. Annular dielectric sealing members 44 and 45 pervious to electromagnetic fields are also respectively interposed between the modulating-grid supporting members 42 and 42a and between a reflector electrode supporting member 26a and anode 12 to hermetically seal the resonator gap regions 16 and 25 respectively. A direct voltage insulating connection comprising an outstanding flange portion 26b of reflector electrode supporting member 26a, a similar flange portion 42b of modulating grid supporting member 42a and an annular insulating spacer 43 is included to enable different unidirectional operating potentials to be applied to the input and output resonators associated with the device. Another direct voltage insulating connection 46 is also provided between the anode 12 and an output cavity resonator 23a.

With the construction illustrated in Fig. 2, the electron beam forming and controlling portion of my invention may be constructed as a separate unit 47 which may be inserted within suitable input and output radial cavity resonators such as resonators 17a and 23a which are constructed to have suitable contact making fingers 48 defining central apertures through which the electron beam forming unit 47 may be inserted. Fingers 48 are arranged to make contact with the appropriate electrodes of the discharge device 10a, as indicated. In the device of Fig. 2, I have included means for regeneratively coupling a fraction of the energy produced in output resonator 23a back to input resonator 17a in order that device may operate as an oscillator. A section of concentric line 49 terminating in suitable coupling disks 50 and 51 communicates between input resonator 17a and output resonator 23a. A capacitive coupling connection 52 is inserted in the line to enable difierent unidirectional operating voltages to be supplied to the resonators. The connections to battery 31 are similar to that indicated in Fig. 1 with the exception that reflector electrode 26 is preferably connected through tap 33 to a more negative voltage point on battery 31.

.The operation of the electric discharge devices and circuits of my invention described above, can best be understood by reference to the diagrammatic representation of the electron stream movement illustrated in Fig. 3 taken in connection with the schematic circuit diagram of Fig. 4. In the upper portion of Fig. 3, a curve A representing a typical high frequency signal supplied to the input resonator 17 through coaxial cable 19 and coupling loop 18 has been plotted along a horizontal time axis. Below curve A, I have illustrated the electron stream controlling portion of discharge devices or 10a as an apparatus continuing in time for a time interval equal to the period for which the high frequency signal is plotted. In this portion of Fig. 3 the heavy solid lines represent the cathode and anode respectively of the discharge device of my invention, while the consecutive horizontal dashed lines between these heavy solid lines represent the control electrode, modulating electrodes and reflector electrode of the device, as designated. Vertical dashed lines 90 are included to separate the time interval illustrated into time periods of half-cycle duration relative to the input signal.

Consider the period of time designated in Fig. 3 by the numeral 100 when no signal is supplied to input resonator 17 or 17a and no high frequency field is generated in the vicinity of modulating electrodes and 15a. In the absence of such a modulating field, electrons emitted from cathode 11 are focused and accelerated by focusing member 20 and control electrode 22 toward reflector 26. Since the modulating electrodes 15, 15a are held at a high positive potential with respect to both control electrode 22 and cathode 11, the electrons are accelerated as they approach modulating electrodes 15, 15a and pass through the interstices of modulating electrodes 15, 15a into a retarding field produced by reflector electrode 26 which is maintained at a strongly negative potential with respect to modulating electrodes 15, 15a. If reflector electrode 26 is at a sufficiently negative potential, the velocity of these transmitted electrons reduces to zero approximately at the surface of reflector electrode 26. Under these quiescent signal conditions, a distribution of electrons emitted from the cathode results such that concentrations of electrons in front of the cathode 11 and in the vicinity of reflector electrode 26 results. Each of these electron concentrations, illustrated in Fig. 4 and designated by numerals 115 and 116 respectively, produces a corresponding space charge having a potential minimum region therein similar to that which normally exists in low frequency triode or other multi-electrode vacuum tubes. The concentrations of electrons around reflector electrode 26 may be considered for most practical purposes to convert the reflector electrode 26 into a virtual cathode.

If a high frequency field is now introduced in the vicinity of the modulating electrodes by such means as a high frequency signal supplied to input resonator 17 or 17a, there will be a cyclic velocity modulation of electrons passing through this high frequency field. During the first positive half cycle indicated in Fig. 3 by the period 101, electrons designated by dotted block 112 passing through modulating electrodes 15, 15a from cathode 11 will be accelerated to overcome the retarding field in the vicinity of reflector electrode 26 and pass through to be collected by anode 12, as indicated by arrow B. During the next negative-going half cycle period 102 of the high frequency signal, electrons indicated by dotted block 113 passing through the modulating electrodes 15, 15a from cathode 11 are retarded sufficiently to be reflected by reflector electrode 26 back toward the modulating electrodes 15, 15a as indicated by arrow C. If the time of transit of the electrons designated by block 113 in traveling to and from reflector electrode 26 is made equal to 31r/2 radians at the frequency of the input signal, i. e. is made equal to three-quarters of the period of one cycle at this frequency, then these electrons will return back to the modulating electrodes 15, 15a in a time phase such that the initial portion of the returning electrons will be retarded by the positive going signal on the modulating electrodes while the later portion of these returning electrons will be accelerated by the beginning of the negative-going cycle of the succeeding half-cycle of input signal. These time relations are indicated in Fig. 3 by the dotted block 113a which passes under modulating elec.

trodes 15, 15a between the time periods 103 and 104.

If the distance between controlelectrode 22 and modulating electrodes 15, 15a and the operating potentials supplied to these electrodes are such that the time of transit of the reflected electrons passing under modulating electrodes 15, 15a and into the retarding field of the cathode control region of the device during the time period 103 is equal to 31r/2 radians at the frequency of the input signal, these retarded electrons will be rereflected back toward the modulating electrodes 15, 15a. With this transit angle of 37r/2 radians, such re-reflected electrons, indicated by the dotted block 113B, will reach the modulating electrodes 15, 15a at the beginning of the time period designated by the numeral and be traveling in a proper direction to be accelerated by the positivegoing signal on the modulating electrodes during this period. These re-reflected electrons 1133 will be accelerated together with a new group of electrons emitted from cathode 11 and passing under the modulating electrodes 15, 15a during the same time period 105 so as to overcome the potential barrier of the reflector electrode and pass to the anode in an electron bunch or current pulse, as indicated by the combination of shaded block 114 and dotted block 1130. Each succeeding group of electrons emitted from cathode 11 and passing through the modulating electrodes 15, 15a under the influence of the high frequency field produced by an input signal will be subjected to the same influences and follow the same general electron paths, as indicated by the various arrows and differently shaded blocks of Fig. 3. As a consequence, a periodic sorting-out process takes place Within the discharge device such that approximately threequarters of the affected electrons are accelerated to the anode in electron bunches or pulses which occur at the same frequency as the input signal, and only one-quarter of the affected electrons are returned to the cathode in similar periodic pulses.

The above explanation has been predicated upon the existence of theoretically balanced conditions and an ideal transit time angle on both sides of modulating electrodes 15, 15a. Under actual practical operating conditions, only a partial realization of the theoretical distribution described above can, of course, be obtained. Furthermore, the various operating conditions may be purposely modified in order to obtain other modes of operation suited to other desired applications for the discharge device.

In practice, the transit time is determined primarily by the distances and the potential differences between the electiodes involved, and it has been found that although an adjustment of the transit time angle to be approximately 31r/2 radians usually results in optimum efficiency, considerable leeway in the magnitude of this transit time angle is permissible. Satisfactory operation may be accomplished with devices Whose distances and operating potentials are adjusted such that the transit angle is anywhere from 2.51/2 radians to 3.51r/2 radians.

The construction and distances between the various electrodes and the operating potentials which must be supplied thereto in order to provide the proper transit-time angle, can be determined by methods generally known in the art and set forth in many text books upon the design of velocity modulated discharge devices. A further discussion of this problem in design is not, therefore, believed necessary here. In general, the greater the distance between electrodes, the greater the transit-time angle; and the higher the potential difference between the electrodes, the higher the electron velocities and the smaller the transit-time angle. In connection with this problem, it should be noted that the intensity of the retarding electric field in the reflector electrode control region 116 is determined primarily by the potential difference between the voltage supplied to reflector electrode 26 and modulating electrodes 15, 15a. Anode 12, although maintained at a high positive potential with respect to reflector electrode 26 exerts negligible effect upon this control field since reflector electrode 26 acts as a shielding electrode from the influence of the anode voltage.

mean

The degree of electron velocity modulation and electron stream control described above depends to a large measure upon the magnitude of the high frequency field produced by the modulating electrodes 15, a. The virtual cathode comprising the space charge region in the vicinity of the reflector electrode 26 functions in the same manner as a true thermionic cathode to contribute electrons to the cathode-to-anode current in accord with the intensity of the modulating field. Moreover, the degree of excitation of output resonator 23 is directly dependent upon the concentration of the electron bunches passing to the anode and, therefore, represents the intensity of the input signal supplied to the input resonator 17.

Depending upon the potential difference between the reflector electrode 26 and the modulating electrodes 15, 15a, the device may be operated either as a class B or class C amplifier. With the reflector electrode 26 maintained slightly negative with respect to the modulating electrodes, the device may be held at the anode current cut-off point to simulate class B operation. tion is illustrated in the diagrammatic representation of Fig. 3 described above. Class C operation can be simulated by maintaining the anode at a potential more negative with respect to the modulating electrodes than for class B" operation.

The operation of the oscillator shown in Fig. 2 is identical with the above-described operation as an amplifier, with the exception that the input signal is derived from a portion of the electromagnetic field energy generated in output resonator 23a. Since a strong signal normally is fed back to the input resonator through concentric line 49, it is usually preferable for best efliciency to maintain the reflector electrode at a fairly negative potential with respect to cathode 11 and control electrode 22. The frequency of oscillation is determined primarily by the natural resonant frequency of the cavity resonators 17a and 230.

As can be seen from the above description of the operation of my invention, the frequency of operation is fixed almost entirely by the natural resonant frequency of the cavity resonators associated with the device. Although a variation in anode voltage and especially in reflector voltage may have considerable effect upon the quiescent value of operating current and a slight effect upon the transit time angle, the frequency of operation and the general efliciency of the device will not be greatly affected by small changes in such anode or reflector electrode voltages.

In general the discharge device of my invention operates in a manner somewhat similar to space-chargecontrolling low frequency triode or multi-electrode discharge devices. However, the space charge region which is effectively controlled by the modulating electrodes is located in the vicinity of the reflector electrode 26. The modulation of this reflector electrode space charge region designated by numeral 116 in Fig. 4, is accomplished by modulating electrodes 15, 15a that are located between the electron emitting member and the space charge region which is to be controlled. This fact enables a very great control of the space charge with a' relatively little exertion of input signal energy. A similar location of the modulating electrode between the cathode and the current limiting space charge region is exceedingly difficult, if not impossible, to obtain in conventional low frequency devices.

It will thus be seen that I have provided improved reflex type velocity modulated electron discharge devices and circuits which constitute amplifiers or generators of high frequency electric energy. It is to be understood that although I have shown particular embodiments of my invention many modifications may be made and I intend by the appended claims to cover all such modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A high frequency electric discharge, device comprising, an electron emissive cathode, a collecting anode toward which emitted electrons are directed, means including a modulating electrode located intermediate said cathode and said collecting anode for velocity modulating said electrons in accord with a high freuency signal, a reflector electrode located intermediate said modulating electrode and said collecting anode,

This situameans associated with said electrodes for connecting said electrodes to unidirectional voltages to maintain said modulating electrode at a positive potential with respect to said cathode and said reflector electrode, said modulating electrode being spaced from said cathode and said reflector electrode by distances such that relative to the unidirectional voltages applied to the electrodes a substantial portion of electrons velocity modulated by said modulating electrode are reflected by said reflector electrode back to said modulating electrode during a transit-time in the neighborhood of 31r/2 radians and are re-reflected by said cathode back to said modulating electrode during a transit time in the neighborhood of 31r/2 radians where the time of one cycle of said high frequency voltage is represented by 21r radians, whereby bunches of electrons including said re-reflected electrons are accelerated to reach said collecting anode at a frequency dependent upon the frequency of said signal, and output means associated with said collecting anode and energized by said electron bunches passing to said collecting anode.

2. A high frequency electric discharge device comprising a plurality of electrodes including an electron emissive cathode, an anode toward which electrons emitted from said cathode are directed, a modulating electrode located intermediate said cathode and said anode for velocity modulating said electrons in accord with a high frequency signal voltage impressed upon said modulating electrode, and a reflector electrode located intermediate said modulating electrode and said anode, means for connecting said electrodes to unidirectional voltages to maintain said modulating electrode at a positive potential with respect to said cathode and said reflector electrode, said electrodes being spaced to provide with said relative unidirectional potentials supplied thereto, respective electron transit-time angles between said cathode and said modulating electrode and between said modulating electrode and said reflector electrode which transit-time angles lie between 2.51r/2 radians and 3.51/2 radians at the frequency of said signal voltage, whereby a substantial portion of velocity modulated electrons are reflected by said reflector electrode back to said modulating electrode and are re-reflected by said cathode back to said modulating electrode in a time phase to be accelerated by said modulating electrode to reach said anode in electron bunches at a frequency determined by the frequency of said signal voltage, and an output cavity resonator arranged to be energized by said electron bunches passing to said anode.

3. A high frequency electric discharge device comprising, an electron emissive cathode, an anode, means for forming a beam of electrons directed toward said anode, an input cavity resonator, a pair of modulating electrodes connected to said input resonator and arranged to velocity modulate the electrons of said beam in accord with a high frequency field within said input resonator, a reflector electrode arranged to influence the beam of electrons passing from said modulating electrode to said anode, means for supplying a high positive voltage to said modulating electrodes relative to said cathode and said reflector electrode to produce separate retarding fields in the neighborhood of said cathode and said reflector electrode respectively, the distances between said anode, cathode, and modulating electrodes and the voltages supplied thereto being such that a substantial portion of electrons velocity modulated by said modulating electrodes and passing under the influence of said modulating electrodes from opposite directions are reflected by said retarding fields back to said modulating electrodes with a transit-time angle in theneighborhood of 31r/2 radians at the frequency of said high frequency field whereby said reflected electrons return to said modulating electrodes after two reflections in a time phase to be accelerated together with a second substantial portion of emitted electrons to reach said anode in electron bunches, and an output cavity resonator arranged to be energized by said electron bunches passing to said anode.

4. A high frequency electric discharge device comprising, an electron emissive cathode, a reflector electrode, means for forming a beam of electrons directed toward said reflector electrode, an input cavity resonator, a pair of modulatingvelectrodes connected to said input resonator and arranged to velocity modulate the electrons of said beam in accord with a high frequency field within said input resonator, means for supplying a high positive voltage to said modulating electrodes relative to said cathode and said reflector electrode to produce separate retarding fields in the neighborhood of said cathode and said reflector respectively, the distances between said reflector electrode, cathode, and modulating electrodes and the voltage supplied thereto being such that a first substantial portion of electrons velocity modulated by said modulating electrodes and passing under the influence of said modulating electrodes from opposite directions are reflected by said retarding fields back to said modulating electrodes with a transit time angle in the neighborhood of 31r/2 radians at the frequency of said high frequency field whereby said reflected electrons reach said modulating electrodes after two reflections in a time phase to be accelerated together with a second substantial portion of emitted electrons to reach said reflector electrode in electron bunches, and an output cavity resonator arranged to be energized by said electron bunches passing to said reflector electrode.

5. A high frequency amplifier comprising an electron discharge device having a cathode, an anode, focusing means for forming a beam of electrons directed toward said anode, an input cavity resonator, a pair of modulating electrodes connected to said input resonator and arranged to modulate the velocity of electrons of said beam in accord with a high frequency field in said input resonator, input coupling means for establishing a high frequency field in said input resonator responsive to a signal voltage, a reflector electrode interposed between said modulating electrodes and said anode, an output cavity resonator connected between said reflector electrode and said anode to be energized by electrons passing to said anode, output coupling means for extracting energy from said output resonator, a source of unidirectional voltage connected to maintain said modulating electrodes at a positive potential with respect to said cathode and said reflector electrode, said discharge device having an electron transit time angle between said cathode and said modulating electrode in the neighborhood of 311'/ 2 radians and having a transit time angle between said modulating electrodes and said reflector electrode in the neighborhood of 31r/2 radians whereby a substantial portion of velocity modulated electrons are reflected by said reflector electrode and are re-reflected by said cathode to pass to said anode in electron bunches responsive in magnitude and frequency to the field in said input resonator.

6. A high frequency oscillator comprising, an 616C307 discharge device having a cathode, an anode, focusing means for forming a beam of electrons directed toward said anode, an input cavity resonator, a pair of modulating electrodes connected to said input resonator and arranged to modulate the velocity of electrons of said beam ll accord with a high frequency field in said input resonator, a reflector electrode interposed between said modulating electrodes and said anode, an output resonator connected between said reflector electrode and said anode to be energized by electrons passing to said anode, output coupli z means for extracting energy from said output resonator, a source of unidirectional voltage connected to maintain said modulating electrodes at a positive potential with respect to said cathode and said reflector electrode, said discharge device having a transit time angle between said cathode and said modulating electrodes in the neighborhood of 31r/ 2 radians and having a transit time angle between said modulating electrodes and said reflector electrode in the neighborhood of 31r/2 radians whereby a substantial portion of velocity modulated electrons are reflected by said reflector electrode and are re-reflected by said cathode to pass to said anode in electron bunches responsive in frequency to a field in said input resonator, and high frequency energy coupling means from said output resonator to said input resonator for establishing a high frequency field within said input resonator with a fraction of the energy produced in said output resonator.

7. A high frequency amplifier comprising, an electron discharge device having a cathode, an anode, focusing means for forming a beam of electrons directed toward said anode, an input cavity resonator, a pair of modulating electrodes connected to said input resonator and arranged to modulate the velocity of electrons of said beam in accord with a high frequency field in said input resonator, input coupling means for establishing a high frequency field in said input resonator responsive to a signal voltage, a reflector electrode interposed between said modulating electrodes and said anode, an output resonator connected between said reflector electrode and said anode to be energized by electrons passing to said anode, output coupling means for extracting energy from said output resonator, a source of unidirectional voltage, said cathode and said reflector electrode being connected to receive voltages from said source and said modulating electrodes being connected to receive a voltage from said source that is positive with respect to the voltage supplied to said cathode and said reflector electrode, said modulating electrodes being spaced from said cathode and said reflector electrode by distances such that a substantial portion of electrons velocity modulated by said modulating electrode are reflected by said reflector electrode to return to said modulating electrode during a transit time in the neighborhood of 31r/ 2 radians and are re-reflected by said cathode back to said modulating electrode during a transit time in the neighborhood of 3'1r/2 radians whereby said re-reflected electrons reach said modulating electrode in a time phase to be accelerated to reach said anode in electron bunches at a greguency equal to the frequency of said input resonator e References Cited in the file of this patent UNITED STATES PATENTS 2,278,210 Morton Mar. 31, 1942 2,337,214 Tunick Dec. 21, 1943 2,406,370 Hansen et al. Aug. 27, 1946 2,413,251 Smith Dec. 24, 1946 2,425,748 Llewellyn Aug. 19, 1947 2,445,771 Fremlin July 27, 1948 2,457,495 Rochester Dec. 28, 1948 2,459,283 McNall Jan. 18, 1949 2,476,765 Pierce July 19, 1949 2,482,769 Harrison Sept. 27, 1949 2,570,289 Touraton Oct. 9, 1951 OTHER REFERENCES Maximum Efliciency of Reflex Klystron Oscillators, Linder and Sproul, Proceedings of I. R. E., March 1947, reprinted by R. C. A.; pages 246-247 relied on. 

